The invention relates in general to a reinforced electrically conductive cable and in particular to an electrical cable having a single yarn high modulus organic fiber strength member surrounded by metal conductors.
Conventional electrical cables of the type used in household electric cord sets are manufactured from stranded copper wire surrounded by a filler material, such as paper, jute, cotton or rayon. The filler material reduces the amount of jacket material required for the cord and is typically helically wrapped about the stranded copper conductors. An insulator, such as a polyvinylchloride jacket, is extruded over the filler material to complete the cord.
Unfortunately those household cord sets suffer from several drawbacks. At present, there is a requirement that household electric cord sets have sufficient tensile strength to withstand a tensile force of 170 pounds. The primary strength providing members in prior art cord sets are the conductors and the filler material within the cord set, which may fail under the stress of such a force.
In addition, it has become relatively expensive to manufacture cord sets using paper and jute fillers. The paper and jute fillers are meant to occupy volume, as well as provide tensile strength within the cable, so that for a given outside diameter of a cable jacket less polyvinylchloride insulation is required, thereby saving money. It is often necessary for an electric plug or connector to be attached to the cord. As a result, the outer layer of polyvinylchloride insulation must be removed completely without nicking or damaging the copper wire conductor strands and causing a loss of conductivity which may result in an increase in the resistivity of the wire. Such an unwanted increase in resistivity may cause the wire to overheat when it is connected to a low impedance electrical load. As a result, it is necessary to remove the insulating polyvinylchloride layer manually, after which the jute or paper filling is removed manually. Attempts to automate the labor-intensive insulation stripping process have met with little success because complete removal of the insulation and filler often results in damage to the underlying conductors.
Cords with multiple insulated leads conventionally have an outer jacket of polyvinylchloride, which holds the leads together and provides additional protection against damage. To achieve a given overall cord thickness and fill the grooves between leads, paper or jute fillers are bundled with the inner leads and a polyvinylchloride jacket is extruded around the bundle, thereby reducing the amount of polyvinylchloride used. These fillers result in the same obstacles to automated stripping as mentioned above.
In addition, such fillers do not have the flexibility that polyvinylchloride has, and so add to the stiffnness of the cord. To retain maximum flexibility, the grooves between leads would have to be filled with polyvinylchloride, which would make the cable unnecessarily heavy.
Co-axial cords are known which contain organic foam. However, because the purpose of the foam is to improve electrical transmission through the dielectric properties of the foam, the foam is extruded in contact with the conductive metal of the cord. The foam is not used as a filler material between two non-porous, insulating jackets, as paper or jute are used as mentioned above.
What is needed, then, is an improved electrical cable or cord strong enough to withstand a tensile force of 170 pounds or more, requiring a minimum of polyvinylchloride, retaining maximal flexibility and minimal weight, and which may be stripped of insulation quickly and easily in order to expose the copper conductors for connection to plug assemblies, connectors and the like.